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Old 06-26-2022, 03:42 PM   #1
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dash A/C 3500 express

almost to the end of this one.
chevy 3500 express cutaway that had dash and auxiliarialy A/C.
owner wanted the extra stuff gone to get rid of the underskirts condensor.
yes i started another thread about this but this was what i thought i started but guess not.
been a pain more than an adventure.
ending up with a condensor from lkq that i cleaned and flushed a compressosor from a local pull it yard.
drained the compressor and re filled it with PAG 46 oil before install and used brand new lines from parts geek.
that problem is they do not come with new seals. my local oreilly had them suprisingly but i had to by the whole pack. not bad at 15$ for it.
ok knew lines from parts geek a junkyard condensor and compressor.
for the ones that know.
high pressure switch id built on the back of the compressor and almost not accessible.
my problem is i am not getting the contol signal to the fuse box/or from the pcm to trigger the compressor clutch.
but i can hardwire the clutch and get 50-60 degree air?
wanna start looking at the dash switch but i have never taken a dash panel or door panel apart that ever went back togeter correct?
i think the signal comes from my dash switch but my haynes BS manuel wiring says otherwise?
new post so i might be able to figure out how to post my books wiring diagrams.
i can make the A/C work just aint getting the compressor clutch signal.
all relays test good and all wires ohmed out as fine so that lead me to the dash switch.
many of mis labeled fuses in these boxes.
igntion E runs your turn signals as well as other things.

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Old 06-26-2022, 04:09 PM   #2
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are you getthing the A/C enable from the dash controller? im assuming yes but the coach buoilder may have done some voodoo for the rear A/C and ran the dash signal through the skirt condensor pressure switch so it would be lost before it makes it to you. the trick may be in looking for the original; wires or at least where you stubbed them off.. its pretty common to have the pressure switch inside the skirt condensor and it wouldve been a high /lo so it would be a single pair of wires...
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Old 06-26-2022, 05:37 PM   #3
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no sir.
i didnt do the original demo.
the only wire i have found cut and was missing about 2 foot was to the compressor clutch from original harness to connector and have ohmed it out so know i am on the right wire.
no power to the harness power side.
played with the relay and all is good just not getting the command to the relay.
i have wiring diagrams but havent taken pictures to post yet.
my high pressure switch is in the compressor which is a pain to even look at.
my low pressure switch is on the side of the accumulator and a pain to ohm out but is good.
i started there because it breaks ground to the clutch if out of range.
have tracked everything back to no activation signal to relay.
gonna try looking at the dash switch next?
caint find a pcm pin out for mine yet?
i have bolt on pcm connections and everything online is green and blue plug and play stuff.
i do have one wire cut and the corresponding wire close by and the colors match but connecting them didnt change anything.
but there are at least 7 other wires the same colors and if i go back to my chiltons/haynes manual it doesnt give me the pin out and its wire colors match closer to on line but not really.
i can hard wire the compressor with roach clips and everything is good.
can see both pressure switches.
but no command?
i assume the dash knob has to send the signal to the PCM to send it out.
i will try to post wiring diagram post soon.
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Old 06-26-2022, 07:13 PM   #4
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for some reason i had thought the Low / high pressure switch on these goes through the PCM.. on some of these GM's it sets a code that has to be cleared before the PCM will give a green light to the A/C.. im thinking id try to read codes and see if there is one related to the A/C. A/C codes usually wont turn on the CEL light so the only way to know would be to read it out...
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Old 06-27-2022, 09:41 AM   #5
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Was there 2 separate systems/compressors, or was there only one? If only one for both front and rear unit, your underskirt condenser and all the rear units very likely piggybacked on the factory stuff. So any switches might have to be properly bypassed.

Like christopher suggested, GM also interfaced the ac system through the pcm, so they could disable it during full throttle or engine overheating. Some systems sent all the info to the pcm, and let the pcm control the relay outright. Other systems the pcm would feed clutch relay power through the ac switch, then low and high pressure cutouts, and then to the relay. In my experience it's all through a relay though, as the clutch should get power from a relay, regardless of how the control is setup, so see if your relay has power to it/through it. See if you can find a clutch relay in the fuse box, and there should be a fuse feeding that as well. In the old days, relays were pretty reliable and robust, recent years they've become unreliable, so don't just check for clicks, make sure it passes current.

What year you working on?
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Old 06-27-2022, 04:37 PM   #6
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yes from underhood block power out to compressor clutch and ground from clutch is broke by the low pressure switch grounding to the pcm.
the body fuse block powers the dash switch and is broken by the high pressure switch to the pcm.
evrything works with the clutch staight wired it just not seeing a signal to the relay.
i will when i get time probably next weekend will try the scan tool.
thanks
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Old 06-27-2022, 04:58 PM   #7
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sorry booyah i missed your post. it a chevy 3500 express 6.0.
i have checked power to the relay and have ohmed out the wiring from relay to clutch connector.
it was just one compressor feeding both systems.
my low pressure switch is on the accumulator and my high pressure switch is on the back of the compressor.
with the clutch hard wired i let everything blow wide opinion in max A/C for at least an hour and watched my manifold and high and low steadied out within a few minutes and stabilized completely within 5 minutes and never moved from there while running.
it wasnt as hot as it had been earlier in the day it had started cooling down before i decided to jump the clutch. but it was still 95 in the bus and i forgot to put a fan in front of the condensor to simulate road air being forced in.
coolant got up to working temp and the system was pushing 51 to 55 air in the outlets closest to the blower and an average of 58-60 on the 2 farthest away.
i am still trying to find the correct pin out for my pcm.
everything i can find online has two seperate connectors that are clip on my pcm has a solid bar bolt on connector but one thing i thought of today is that i have been looking for 2004 stuff but the chassis left GM as a 2003. according to my manual without a pin out shows the clip on style connectors instead of what i have.
its obvious that the previous owner/owners?
had the pcm replaced at some point because it was just dangling and had a few wires never reconnected and i have a green white wire that is not connected and i found the other end but nothing changed.
my wiring diagram says my relay to pcm is green and white.
i will reconnect and dig out my scan tool or maybe its time to upgrade my old one.
i would like to get this fixed or at least water proof that little nub of wire i was left so i can get the pcm twisted turned and shoved behind everything back into its holder.
thanks for everyones advice.
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Old 06-28-2022, 07:45 AM   #8
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what was your idle? air in the 50s isnt bad if all the doors and windows are open but if the windows were closed thats not very cool at the far vents.. is the liquid line temp staying cool or is it getting hot?.. im used to tuning in GM's to get air well down into the 40s..
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Old 06-28-2022, 07:56 AM   #9
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With that info, ac clutch relay is controlled by pcm. All switches input to pcm. All Van pcm's from that time period that I can recall had 2 pcm connectors, they were long and stacked one on the other. Maybe you got the wrong box? Should be under the hood on the left fender.

According to prodemand.

20A HVAC fuse -(BRN)- Dash Switch -(LT GRN)- High pressure switch -(DK GRN)- PCM pin 17

10A IGN E fuse - Relay Coil -(DK GRN/WHT)- PCM pin 43

10A A/C fuse - Relay Control -(DK GRN)- AC clutch coil -(BLK)- GND

PCM pin 55 -(DK GRN)- low press switch -(BLK)- GND

HTH, good luck
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Old 06-28-2022, 04:11 PM   #10
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tried to upload pics but it isnt working for me.
but the box is under the hood under the master cylinder just behind the coolant jug.
and i just looked and my broke wire is on the 17 pin so this weekend i will get it back together and get the clutch wiring back together and try to check for codes to reset.
my scan tool and my sons scan tool is not seeing anything related to an A/C code.
might finally be time to upgrade my scan tool.
i would love one that reads mileage but i think thats a worthless effort because i know before i bought it the guage cluster was changed because of a fluctuating oil pressure guage. got it home and change the sensor and no more fluctuation.
and found the pcm just dropped down in it and not secured so started looking and found one wire cut?
so whoever before me disabled the A/C went out of the way to disable it.
i know the compressor is a royal pain to get to but its doable so why cut the damn wires and why cut the pcm wire?
anyway thanks for the help. it will be saturday before i get back to it.
and my 17 pin is a green white so we will try again.
thank ya
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Old 06-28-2022, 04:18 PM   #11
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also i found out because when i bought and drove it home that it had no turn signals.
the ignition E fuse runs my turn signals and whatever else apparantly.
put a fuse in a boom turn signals work.
i always get the bastard child to deal with like we only work on that bus on fridays that we dont give a damn on.
you pissed off at management? go work on bus 766 you know where its at.
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Old 06-29-2022, 06:55 AM   #12
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Quote:
Originally Posted by Jolly Roger bus 223 View Post
also i found out because when i bought and drove it home that it had no turn signals.
the ignition E fuse runs my turn signals and whatever else apparantly.
put a fuse in a boom turn signals work.
i always get the bastard child to deal with like we only work on that bus on fridays that we dont give a damn on.
you pissed off at management? go work on bus 766 you know where its at.

766 is the number my RedByrd had in its district



all school busses are bastard-children.. even back to the days of my Loadstar... I have all the books and and CD's and damned if half the stuff doesnt match the diagrams and descriptions..
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Old 07-02-2022, 01:37 PM   #13
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a little update but not much because we had a tropical storm form and come in with rain around noon so i got wires connected and heat shrinked.
whoever did the A/C delete before me really went out of there way?
on the PCM i did find a wire on pin 17 as pointed out by boohyah thank you sir cut.
no one i have talked to has or even have heard of a scan tool that can read air conditioning codes?
so i disconnected the battery before i connected the pcm and compressor clutch wires that were also cut.
was looking for a temp sensor that could be cutting out the control signal like ambient air but havent found one?
my wiring diagram doesnt show one and the only other thing i can find is the air box door and motor (but i am not having those issues) air temp actuator. and not tied to the pcm.
it is tied into the dash switch and brakes power to the dash switches but the blower works as should and nothing air door is tied into the pcm except through the dash switch so if my this morning stuff dont work then its on to opening the dash which i hate? except on the big stuff?
i have never opened a vehicle plastic dash or door panel and got it back together perfect?
i am also going to look again at the high pressure switch on the back of the compressor i have checked the wiring before i put the compressor in but i diddnt check the switch.
in this one i had to plug it in before the compressor was ever bolted in.
to replace it in place will be as many expletive that we can come up with even if its on a lift.
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Old 07-02-2022, 03:34 PM   #14
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now learning that i might have an early lq 6.o verses the ls engine? wiring diagram
show some of the same but nothing with what i am playing with?
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Old 07-02-2022, 03:42 PM   #15
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shouldnt matter much for my problem
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Old 07-03-2022, 01:07 PM   #16
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ok i kind of feel stupid at this point.
reconnecting the pcm wire had no effect so i went to look at the high pressure switch again but i cant even get my hand in there to pull the connector and jump it to see if it makes a difference without un bolting the compressor and pulling the belt to slide it forward maybe enough to brake my arm to diconnect it. and bolt it back up belt back on jumper the connector to see if it makes a difference.
and if the switch proves bad then it is compressor mounted and i have to recover the charge and almost pull the compressor again just to access it to change it.
so i started second guessing my charge pressure.
i was at 250 high and 50 low with the clutch hot wired on.
up to this point no one has been able to tell me what pressures i should be seeing off or on (i didnt ask here yet).
but at looking up new high pressure switches orielly only has two and one is like 255 on and 460 off? and the other is 265 on and 475 off?
i saved my old compressor and pulled the switch and the color matches for there higher 265 on switch.
the replacement compressor switch doesnt match either color (purple for 260 switch and red for the 265)that has a stated pressure rating.
ok here comes my questions.
mainly for chris and boohyah but of course anyone else with the knowledge.
my high pressure switch is a nightmare to get to so i would like to know what actual pressures i should see with engine off and if i have to jump the clutch again what i should see with engine on and clutch engaged for pressures.
in my work we normally see lower pressures while compressor of and higher while compressor on so there description doesnt make since.
i had to loan my charge recovery machine out and didnt get it back yet and standing charge without clutch lock up engine running or not is 110 both high and low sides.
wont take any more from the bottle liquid or vapor.
i need to know the correct pressures if yall can help.
and christopher my son that i had locked in the bus with a temp gun said he was seeing the mid 30-s to 40-s in the dash and i trust him i only posted what i saw in the beginning's with the doors open.
just cant figure out why i am not getting a clutch signal?
guess open the dash in the morning cause it is what triggers the high pressure switch to the pcm.
i think my pcm is looking for a higher pressure to trigger the switch since my old switch is 265 but had dash and auxilliary?
still have found a scan tool that can read A/C codes except videos online from across the pond that could do every vehicle in the world.
i hate to just splice the pressure switch wiring where i can get to it? not fun but easier to do than pulling the compressor again or at least un bolting it enough to move it enough to get my hand on the connector. as is mounted it is almost directly up against a solid front axle inside of the suspension mounts
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Old 07-03-2022, 01:48 PM   #17
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but if my high pressure switch and wiring was bad and dash signal was bad why am i able to jump the compressor clutch and make it work?
that shouldnt override the other safeties but it did?
yes i found a pcm related wire cut and i reconnected yes i found a clutch wire cut and i reconnected?
i have found nothing else cut and have ohmed out from fuse box to connector.
if i can get a definite on working pressure then either i pull the compressor enough to jump the connector for high pressure and prove it bad and pull the dash to make sure its sending signal before i drop the charge. this stuff in my 30lb bottle isnt easy to come buy and i dont have a recovery jug for 134?
will have to clean my recovery machine and a new bottle. i have a brand new recovery tank on my truck but it has already had 410 in in and probably some residual so hate to use it and mix things?
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Old 07-03-2022, 07:23 PM   #18
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Quote:
Originally Posted by Jolly Roger bus 223 View Post
but if my high pressure switch and wiring was bad and dash signal was bad why am i able to jump the compressor clutch and make it work?
that shouldnt override the other safeties but it did?
yes i found a pcm related wire cut and i reconnected yes i found a clutch wire cut and i reconnected?
i have found nothing else cut and have ohmed out from fuse box to connector.
if i can get a definite on working pressure then either i pull the compressor enough to jump the connector for high pressure and prove it bad and pull the dash to make sure its sending signal before i drop the charge. this stuff in my 30lb bottle isnt easy to come buy and i dont have a recovery jug for 134?
will have to clean my recovery machine and a new bottle. i have a brand new recovery tank on my truck but it has already had 410 in in and probably some residual so hate to use it and mix things?

I have several recovery bottles.. I like to keep my refrigerants separated.. I do have one bottle that is mixed which ill take to a recycling center and have emptied... when I recover a system i'll usually measure the vapor pressure of the system and see if it matches the chart... if its real close i figure the refrigerant to be pure and worth saving (where i could use it again).. I never save refrigerant from a burned up compressor... in a house the electrical arcing that occurs in a burnout can turn the freon acidic.. in a vehicle theres often graphite and metals in the oil / refrigerant..



to me if your high pressure switcvh was bad o nthe compressor then it wo0uldnt engage.. at least thats how the GM compressors with internal switches ive dealt with are... there was still just 1 (or 2) wires going to the compressor.. .. the fact it engages and cools says the internals and electricals of the compressor are fine.. but the computer is the culprit..



whats interesting is people saying their scan tools dont read A/C codes.. ive seen them on my scan tools when working on cadillacs anyway... pressure switch inputs almost always tossed a code.. actually a tahoe with a 5.3 I did the A/C on, showed a low pressure code because it was unplugged.. if it were mine, the next step would be making sure there is a proper signal from the dash control making it all the way out.. it would not surprise me if the aftermarket company spliced into the dash control wire with the pressure switches on the skirt condenser (usually a high / low combo).. so with the skirt unit gone, that circuit would be open..
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Old 07-04-2022, 08:35 AM   #19
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thanks thats my direction for today if i dont decide to take a break from it.
it is already going to be a short bus day cause i am going to fire up the grill this afternoon.
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Old 07-04-2022, 09:01 AM   #20
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Year: 1991
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Chassis: International 3800
Engine: DTA360 / MT643
Rated Cap: 7 Row Handicap
im not doing much bus work today... im Driving my Superior around today..


with its A/C Maxxed!!
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